Phenolic resins, carboxylic resins and the elastomers containing adhesive

ABSTRACT

An adhesive is disclosed for use in flexible circuitry, laminates and electrical products. The adhesive has improved flexibility and adhesive properties. It may be applied in solution form or may be cast as a free-standing film which is later heated and compressed to give adhesive properties. The adhesive comprises a phenol-aldehyde resin or other phenolic resin, an epoxy resin and an elastomer.

This is a division of application Ser. No. 701,205, filed Feb. 13, 1985.

BACKGROUND OF THE INVENTION

Heretofore, thermosetting adhesives have exhibited serious deficienciesin bond strength and flexibility when used with certain substrates suchas Kapton (polyimide) film, polysulfone film, copper foil, or nickelfoil. Phenolic adhesives and epoxy-phenolic adhesives suffer frombrittleness and poor adhesion making them unsuitable for use on flexiblesubstrates. These deficiencies, coupled with adhesive failure whenelectrical components are soldered, preclude their usage in manyapplications.

The Watanabe U.S. Pat. No. 3,932,689 shows a composition containing acresol formaldehyde resin, a bisphenol based epoxy compound, anacrylonitrile-butadiene copolymer and several other components. WatanabeU.S. Pat. No. 4,323,659 discloses several compositions containing abisphenol type epoxy resin, an acrylic copolymer, an imidazoleaccelerator and a brominated novolak. These compositions however, do notinclude an ethylene acrylic elastomer.

An object of the invention is to provide an adhesive with theflexibility and adhesion necessary for use with the above mentionedsubstrates.

A further object of the invention is to provide a thermosetting adhesivewith improved bond strength and improved ability to withstand thevarious manufacturing conditions necessary to produce flexible circuitry(e.g., high temperatures, soldering, or etching).

A further object of this invention is to provide an adhesive that may beapplied to film in solution form, or may be cast as a free-standing filmitself to be used as an adhesive in laminated form.

SUMMARY OF THE INVENTION

The present invention relates to an adhesive suitable for use inflexible circuitry and electrical products. The adhesive withstands hightemperatures, soldering and etching. It has improved flexibility andadhesive properties. The adhesive may be applied in solution form or maybe cast as a free-standing film which is later heated and compressed togive adhesive properties. The adhesive comprises a phenol-aldehyderesin, an epoxy resin, and an ethylene-acrylic elastomer.

The adhesive may be applied in solution form since it is in solvent, ormay be cast as an free-standing film to be used as an adhesive in filmform. The liquid adhesive can be used to adhere copper to processedlaminates, or Kapton (polyimide) film to copper foil. After a heattreatment to effect curing, the adhesive composition exhibits high bondstrength, solder resistance, temperature resistance, flexibility andexcellent electrical properties. The adhesive works well in circuitboard manufacture where flexible films must be bonded together to makeboard substrates which subsequently are wired and soldered.

DETAILED DESCRIPTION OF THE INVENTION

The adhesive composition of the present invention comprises or consistsof a phenolic resin e.g. a phenol-aldehyde resin or cashew nut shellliquid polymer, an epoxy resin, and an elastomer. A catalyst can beadded to promote reaction between the epoxy resin and thephenol-aldehyde resin. A co-elastomer may be used where certain specificperformance is desired.

The phenol-aldehyde resin is formed by the reaction of phenol and/orsubstituted phenols with aldehydes. The phenol can have more than onehydroxy group (e.g. resorcinol), and can have hydrocarbon and othersubstituents. More than one substituent can be present. The aldehyde forexample can be furfural or preferably formaldehyde. Thesephenol-aldehyde resins include thermoplastic resins (novolaks, two-stepresins), heat reactive resins, and thermosetting resins (resole,one-step resins). These are formed by reactions of aldehydes withphenols at aldehyde to phenol mole ratios of 0.5 to 0.89 for novolaksand 0.85 to 2.0 for resoles. There can also be employed modifiedphenol-aldehyde resins.

The phenolic resin types employed were heat reactive resins, resoles andnovolaks. These resins may be based for example on phenol, nonylphenol,o-cresol, p-cresol, cresylic acids, cashew nutshell liquid,o-ethyl-phenol, para-tert-butylphenol, octylphenol (e.g. p-octylphenol)or the allylether formed by etherifying the phenolic hydroxyl group oftrimethylol phenol. These resins may be modified with 5 to 40% ofepoxies, nitrile rubber, cashew nutshell liquid, zinc, tall oil,acrylics, phenoxies, or polyvinyl butyral.

The epoxy resin may be a bisphenol A-epichlorohydrin resin, hydantoinepoxy resin or an aliphatic glycidyl ether such as butylglycidyl etheror other epoxy resins such as those shown in U.S. Pat. No. 2,500,600,the entire disclosure of which is hereby incorporated by reference. Theepoxy groups in hydantoin-epoxy are connected to the nitrogen atoms,e.g. by reaction with epichlorohydrin.

The elastomer which has been most successful in an ethylene acrylicelastomer such as Dupont's Vamac. Vamac is made in accordance withGreene U.S. Pat. No. 3,904,588 the entire disclosure of which is herebyincorporated as reference and relied upon. The ethylene acrylicelastomer according to Greene is a copolymer (terpolymer) of ethyleneand methyl acrylate plus a cure site monomer (--R--)_(Z) --COOH. Theelastomers have the formula ##STR1## Thus there can be used a copolymer(terpolymer) of ethylene, methyl (or ethyl) acrylate, and about 0.5 to10 weight percent of a mono alkyl ester of 1,4-butene-dioic acid inwhich the alkyl group of the ester has 1 to 6 carbon atoms, and thecopolymer has about 20 to 35 grams of (--CO₂ --) units per 100 grams ofcopolymer; the copolymer having a melt index of 0.3 to 100 g/10 minutes.For example the copolymers can contain 40-62 weight percent of methylacrylate units. Examples of mono alkyl esters are: propyl hydrogenmaleate, ethyl hydrogen maleate, and methyl hydrogen maleate.

In place of Vamac in the working examples of this specification (seebelow) there can be used in the same amount the terpolymer of ethylene,methyl acrylate and ethyl hydrogen maleate, e.g., the terpolymer ofExamples 2 or 5 of the Greene patent.

Acrylic elastomers such as Hycar 4051 made from various combinationsacrylic acid, acrylate-esters and acrylamide, have also been used.

Nitrile rubber can be used as an elastomer, such as B. F. Goodrich'sHycar 1032 (33% acrylonitrile) and reactive liquid polymers such ascarboxyl-terminated polybutadiene (Hycar CTB), or carboxyl-terminatedpolybutadiene containing acrylonitrile (Hycar CTBN with 10%, 18% or 26%bound acrylonitrile and Hycar CTBNX (contains 18% bound acrylonitrileand additional random carboxyl groups)). The properties of thesecompositions are as follows:

    ______________________________________                                                                            Hycar                                     Polymer       Hycar CTB Hycar CTBN  CTBNX                                     Characterization                                                                            2000X156  (1300X8)    (1300X9)                                  ______________________________________                                        Viscosity @ 27° C.                                                                   35,000    110,000     125,000                                   Brookfield                                                                    RVT #7 20 rpm, cps                                                            EPHR - Carboxyl                                                                             0.042     0.053       0.065                                     Percent - Carboxyl                                                                          1.9       2.37        2.93                                      Molecular Weight                                                                              4000      3200        3400                                    Number Average                                                                Carboxyl      2.01      1.8         2.4                                       Functionality                                                                 Specific Gravity at                                                                          0.9069    0.9483      0.9554                                   20°/25° C.                                                      Refractive     1.5145    1.5142      1.5141                                   Index at 25° C.                                                        Heat Loss - 2 Hrs.                                                                          0.5       1.0         1.0                                       @ 130° C. - %                                                          Unsaturation as:                                                              cis - %       22.1      23.8        16.3                                      trans - %     53.4      64.2        68.7                                      vinyl - %     24.5      12.0        15.0                                      Bound         --        18-19       18-19                                     Acrylonitrile,                                                                Ash - %       0.02      --          --                                        ______________________________________                                    

Vinyl-terminated polybutadiene containing acrylonitrile (Hycar VTBN (16%acrylonitrile and Hycar VTBNX (containing 16% bound acrylonitrile andadditional random vinyl groups)) having the structure ##STR2## where Ais 1,4- or 1,2-butadiene and B is acrylonitrile, or hydroxy-terminatedpolybutadiene containing acrylonitrile (Hycar HTBN containing 10% or 17%bound acrylonitrile), may also be used as elastomers. The Hycar polymerscan be substituted or unsubstituted.

Other elastomers tested were DuPont's Viton which is a fluoroelastomerbased on the copolymer of vinylidene fluoride and hexafluoropropylenewith the repeating structure possibly --CF₂ --CH₂ --CF₂ --CF(CF₃)--;DuPont's Adiprene which is a polyurethane rubber, the reaction productof diisocyanate and polyalkylene etherglycol; DuPont's Hypalon, achlorosulfonated polyethylene which is a synthetic rubber; Borg Warner'sBlendex, a synthetic resinous product; and Arco's Poly B-D which is alow molecular weight liquid polymer based on butadiene containingcontrolled hydroxyl functionality (homo-and copolymers).

The Vamac and Hycar elastomers proved to be the most successful. Theothers failed to form unsupported films or to offer any advantage inadhesive properties over conventional adhesives. In applications wherespecific properties are desired, two or more elastomers may be used. Thecoelastomer ranges from 0 to 25% of the ethylene acrylic elastomerlevel, or from 0 to 20% of the final solids content of the composition.

A catalyst can be added to this system. This catalyst can be one whichpromotes the reaction of the epoxy resin and the phenol-aldehyde resin.A catalyst used with a nitrile-based elastomer can be one which promotesvulcanization of the elastomer. On occasion it can be desirable to usemore than one catalyst.

The catalyst and curing agents include for example 2-methyl imidazole,tetraisopropyl titanate, trimellitic anhydride, pyromelliticdianhydride, Mondur S, Mondur SH, sulfur, mercaptobenzothiazole,tetramethyl thiuramdisulfide, di-ortho-tolylguanidine, N-oxydiethylenebenzothiazole-2-sulfenamide, benzothiazyl disulfide. At presentimidazole catalysts are preferred. Additional suitable imidazolecatalysts are those mentioned in Watanabe U.S. Pat. No. 4,313,654, col.4, lines 45-61.

The adhesive composition is prepared by combining the phenol-aldehyderesin (or other phenolic resin), epoxy resin and elastomer in solution.This may be done by putting each component in solvent and mixing thethree solutions together, or by a general mixing of components andsolvents until a solution is reached.

The ratio of epoxy resin to phenol-aldehyde resin may be from 20 partsepoxy to 80 parts phenol-aldehyde, to 80 parts epoxy to 20 partsphenol-aldehyde. The elastomer may be from 10% to 80% of the finalsolids material. Optimum results are obtained when the epoxy tophenol-aldehyde ratio is 30/70 to 50/50, respectively, and the elastomeris 40% to 60% of the final solids.

The adhesive of the present invention can also be used to produce anunsupported film. This film may be formed by coating the adhesive on arelease medium, drying, and then rolling the film with or without therelease medium. The adhesive may be coated on a substrate, dried, andthen stored on the substrate for future use. The film is later heatedand compressed to give adhesive properties. This permits use of thismaterial in applications where a solvent should not be used.

The composition can comprise, consist essentially of or consist of thestated materials. Unless otherwise indicated all parts and percentagesare by weight.

EXAMPLES

The following examples illustrate the invention in more detail. In eachof the examples, the solids content of the composition was 35% in methylethyl ketone. The composition was coated on 200H Kapton film (polyimidefilm) at a dry film thickness of 0.001 inch. The coated samples weredried in an air circulating oven at 100° C. for 10 minutes. The sampleswere then laminated to 1 oz. RATK copper foil by pressing and rolllamination. The press procedure was as follows: begin with a press @350° F., place samples in at 400 psi, hold at temperature and pressurefor one (1) hour, and then cool rapidly to ambient temperature. Thesamples for roll lamination were made at 4 FPM, 400 psi at 350° F.

These prepared samples were tested for bond strength at ambienttemperature, bond strength after solder exposure of 550° F., anddielectric strength.

Example #1

Phenol was reacted with formaldehyde at an F/P mole ratio of 0.64 withoxalic acid as a catalyst. A 116°-120° (Ball & Ring) meltpoint resin wasproduced. This resin was placed into solution with a brominatedepichlorohydrin-bisphenol A epoxy (Epirez 5183). The weight ratio ofphenolic to epoxy was 50/50. This material was then blended with anethylene acrylic elastomer (Vamac) and Hycar CTBN-1300×13 (26% boundacrylonitrile). The final composition was 22.75% epoxy, 22.75%phenol-aldehyde, 45.5% elastomer (Vamac) and 9% coelastomer (Hycar) byweight. This material was reduced to 35% solids in solvent. The catalyst2-methyl-imidazole was added (0.22% based on solids).

Example #2

Meta-cresol was reacted with formaldehyde at an F/P mole ratio of 0.887with an oxalic acid catalyst. This resulted in a 190° C. (Ball & Ring)meltpoint resin. This resin was blended with butyl glycidyl ether, Vamacand Hycar CTBN. The ratios were identical to Example #1. The solvent andcatalyst levels were identical to Example #1.

Example #3

The resin of Example #2 was blended with Epirez 5183, Vamac and HycarCTBN. The ratios were 18.2% phenol-aldehyde, 18.2% epoxy, 54.5% Vamacand 9.1% Hycar. The solids content was identical to Example #1 but thecatalyst was omitted.

Example #4

The resin of Example #2 was blended with glycidyl methacrylate, Vamacand Hycar CTBN. The ratios, solvent levels and catalysts were identicalto Example #1.

The Table 1 reports the test data on Examples 1 to 4. The values in thecolumn labeled "control" were obtained using a standard adhesive systembased on epoxy resin. The results were obtained by using IPC Method2.4.9, and the SCI Method (described below). Table 2 shows bond strengthdata as an additional series of adhesives obtained using the SCI Method.The data in Table 2 is included to indicate the added scope of theinvention in employing other types of resins.

SCI Method For Testing Fiber Adhesive Laminate Strips

Liquid adhesive was applied on 0.002-in. Kapton Type H polyimide film,by drawing 5×10-in. film strip containing excessive adhesive throughstainless steel rolls. Roll separation was adjusted in order to give anadhesive thickness of 0.0015-0.0020 in. following exposure of theadhesive-coated film in an oven at 105° C. for 10 min. Approximately 1to 2 in. of one of the 5-in. edges was left uncoated to provide agripping surface for the pull testing. After removal from the oven, theadhesive-coated film was checked for tackiness by touch, and for bubblesby visual inspection. Bond strength was determined as follows: copperfoil (1 oz.) was cut into 5×10-in. pieces approximating the size of thecoated film strips. The adhesive-containing face of the film strip wasmated to the copper foil. A temporary bond was achieved by touching twoopposite edges of the film with a hot spatula sufficient to soften theadhesive and achieve bonding.

The foil-film laminates were permanently bonded in an EEMCO press(hydraulic with electric heat, 75 ton capacity, platen size 18×18 in.)as follows. Approximately 40 sheets of 14×14×0.0065-in. Kraft paperforming a bed approximately 1/4 in. thick, were placed on the polishedside of a 14×14×1/8-in. stainless steel panel. On top of the Kraft papertwo 5×10-in. foil-film laminates were placed side by side. On top of thelaminates was placed another 1/4-in. layer of Kraft paper sheets,followed by the polished side of the second 14×14×1/8-in. stainlesssteel panel. This composite was placed in the pre-heated EEMCO press at350° F. and held for 30 min. at 450 psi.

After removal from the press, and after cooling for 15-20 min., the5×10-in. foil-film laminates were cut into four 1×8-in. strips fortesting. The unbonded 1-2-in. margins at one end of the strips werecoated with masking tape for gripping in an Instron tester (Model TT-Cfloor model with 10,000 lb. capacity and 20-lb., full-scale range). A"T" pull method was employed using a Model 3CA pneumatic-action clamp ata crosshead speed of 2 in./min. and a chart speed of 1/2 in./min.Results were recorded in lbs./linear in. Specimens were visuallyexamined for adhesive and cohesive failure.

It is believed that the results obtained using the IPC Method are atruer reflection of the actual bond strength than the results obtainedby the SCI Method. As shown in Table 1, the IPC Method results areapproximately 160-165% of the values obtained using the SCI Method onthe same composition. If the SCI bond strength values in Table 2 aremultiplied by a factor of 1.6 then most of the values are approximatelyequal to the control value bond strength of 5-7 pounds/inch.

    __________________________________________________________________________    Test    Method Used                                                                            Units                                                                              #1  #2  #3 #4   Control                                 __________________________________________________________________________    Bond Strength                                                                         IPC TM650-2.4.9.                                                                       Lbs./In.                                                                           8-9 7-8 7-9                                                                              4-6                                          Roll Laminate                                                                         IPC Method A                                                                  550° F. Solder                                                                  Lbs./In.                                                                            8-10                                                                             10-12                                                                             9-10                                                                             Blistered                                            IPC Method C                                                          Bond Strength                                                                         IPC TM650-2.4.9.                                                                       Lbs./In.                                                                           10-11                                                                              8-10                                                                             9-10                                                                             8-9  5-7                                     Press Laminate                                                                        IPC Method A                                                                  SCI Method                                                                             Lbs./In.                                                                           6.35                                                                              4.73                                                                              6.30                                                                             6.25                                                 550° F. Solder                                                                  Lbs./In.                                                                            8-10                                                                             10-12                                                                             9-10                                                                             Blistered                                                                          8-9                                             IPC Method C                                                          Dielectric                                                                            ASTM-D-149                                                                             KV/Mil.                                                                            3-4 3-5 3-2                                                                              3-7                                          Strength                                                                      __________________________________________________________________________

    __________________________________________________________________________                          SCI Method                                                           Melting Pt.                                                                            Bond Strength                                                                         Bond Strength × 1.6                                                                IPC Method                           Resin Type   Physicals                                                                              Lbs/In. Lbs./In.   Lbs/In.                              __________________________________________________________________________    Para-tert-octylphenol                                                                      85° C.                                                                          5.65    9.04                                            Para-tert-butylphenol                                                                      83° C.                                                                          5.53    8.85                                            Phenol Novolak                                                                             116-120  6.66    10.66      10-11                                Cashew Nutshell Oil,                                                                        90-110° C.                                                                     6.60    10.56                                           Phenol Novalak                                                                Nonylphenol Novolak                                                                         97-101° C.                                                                     5.9     9.44                                            Tall Oil,     90-100° C.                                                                     5.2     8.32                                            Phenol Novolak                                                                O-Cresol Novolak                                                                            99-104° C.                                                                     4.51    7.22                                            M-cresol, P-Cresol,                                                                        O--Ethylphenol,                                                  Novolak      150-165° C.                                                                     4.78    7.65                                            Blendex BTA,*                                                                              100-105° C.                                                                     3.93    6.29                                            Phenol Novolak                                                                Cresylic Acid Resole                                                                        78-88° C.                                                                      3.25    5.20                                            Furfural-Phenol Novolak                                                                    100-105° C.                                                                     3.43    5.49                                            Acrylic-Modified                                                                           105-110° C.                                                                     4.59    7.34                                            Phenol Novolak                                                                Phenoxy-Modified                                                                           105-110° C.                                                                     3.51    5.62                                            Phenol Novolak                                                                Cashew Nutshell                                                                            --       4.56    7.30                                            Oil Polymer                                                                   Resorcinol Novolak                                                                         100-110° C.                                                                     5.63    9.01                                            M-Cresol Novolak                                                                           195° C.                                                                         6.20    9.92                                            Methylon Resin                                                                             --       4.0     6.40                                            Phenoxy PKHH --       5.10    8.16                                            __________________________________________________________________________     *Blendex BTA is a thermoplastic copolymer of                                  methacrylate/acrylonitrile/styrene                                            For each of the resin types tested in Table 2 the following                   characteristics were constant:                                                Resin Wt. Ratio: 22.75%                                                       Epoxy Type: Epirez 5183                                                       Epoxy Wt. Ratio: 22.75%                                                       Elastomer: Vamac C                                                            Elastomer Wt. Ratio: 45.5%                                                    CoElastomer: Hycar CTBN?                                                      CoElastomer Wt. Ratio: 9%?                                                    Catalyst: 2methyl imidizole                                                   Catalyst Wt. Ratio: 0.22%?                                                    The phenol  and substitutedphenol-containing resins in Table 2 contain        solely a phenol reacted with formaldehyde except for the furfuralphenol       novolak, the cashew nutshell oil copolymer, cashew nutshell oil polymer       and the modified phenolic novolaks.                                      

What is claimed is:
 1. A laminate of copper and a polyimide film bondedby an adhesive composition comprising:(a) 4-72% by weightphenol-aldehyde resins or a resin of an ethylenically unsaturatedphenol; (b) 4-72% by weight 1,2-epoxy resin; (c) 10-80% by weight of anethylene acrylic elastomer; wherein the ratio of phenol aldehyde to1,2-epoxy resin is from 1:4 to 4:1.
 2. A laminate according to claim 1wherein (a) is a phenol-aldehyde resin.
 3. The laminate according toclaim 1 wherein the phenol aldehyde resin is an alkylphenol-formaldehyderesin.
 4. The laminate according to claim 2 wherein theisphenol-aldehyde phenol per se or cresol formaldehyde resin.
 5. Thelaminate of claim 1 wherein the 1,2-epoxy resin is bisphenolA-epichlorohydrin, hydantoin epoxy, or an aliphatic glycidyl ether. 6.The laminate of claim 1 wherein the ethylene acrylic elastomer is acopolymer of ethylene, methyl or ethyl acrylate and a cure site of theformula R₁ OOC--C═C--COON where R₁ is an alkyl group of 1 to 6 carbonatoms.
 7. The laminate of claim 6 wherein the elastomer contains 0.5 to10 weight percent of the cure site monomer units and 40 to 62 weight %of methyl or ethyl acrylate units.
 8. The laminate of claim 1 whereinthe adhesive composition includes a catalyst promoting the reaction ofthe phenol-aldehyde and the 1,2-epoxy resin.
 9. The laminate of claim 8wherein the catalyst is an imidazole.
 10. A laminate according to claim1 wherein a portion of the ethylene-acrylic elastomer is replaced by anitrile-based elastomer and wherein not over 25% of the ethylene-acrylicelastomer is replaced by the nitrile based elastomer.
 11. The laminateaccording to claim 1 wherein the adhesive composition comprises:(a)4-72% by weight phenol aldehyde or a resin from an unsaturated phenol;(b) 4-72% by weight 1,2-epoxy resin; (c) 10-80% by weight of a copolymerand ethylene, an alkyl acrylate selected from methyl and ethyl acrylate,and from about 0.5 to 10 weight percent of a mono alkyl ester of1,4-butenne-dioic acid in which the alkyl group of the ester has 1 to 6carbon atoms, said copolymer having from about 20 to 35 grams of (--CO₂--) units per 100 grams of copolymer, said copolymer having a melt indexof about 0.3 to 100 g/10 min.
 12. The laminate of claim 11 wherein saidmono alkyl ester of 1,4-butene dioic acid is: methyl hydrogen maleate,ethyl hydrogen maleate, or propyl hydrogen maleate.
 13. The laminate ofclaim 12 wherein the alkyl acrylate units comprise about 40 to 62%weight percent of the copolymer.
 14. The laminate of claim 11 wherein(a) is a phenol-formaldehyde or cresol-formaldehyde resin.
 15. A circuitboard comprising films bonded together by an adhesive compositioncomprising:(a) 4-72% by weight phenol-aldehyde resin or a resin of anethylenically unsaturated phenol; (b) 4-72% by weight 1,2-epoxy resin;(c) 10-8% by weight of an ethylene acrylic elastomer; wherein the ratioof phenol-aldehyde to 1,2-epoxy resin is from 1:4 to 4:1.
 16. A circuitboard according to claim 15 wherein (a) is a phenol-aldehyde resin. 17.The circuit board according to claim 15 wherein the phenol aldehyderesin is an alkylphenol-formaldehyde resin.
 18. The circuit boardaccording to claim 16 wherein the phenol-aldehyde is phenol per se orcresol formaldehyde resin.
 19. The circuit board according to claim 15wherein the 1,2-epoxy resin is bisphenol A-epichlorohydrin, hydantoinepoxy, or an aliphatic glycidyl ether.
 20. The circuit board of claim 15wherein the ethylene-acrylic elastomer is a copolymer of ethylene,methyl or ethyl acrylate and a cure site of the formula R₁OOC--C═C--COOH where R₁ is an alkyl group of 1 to 6 carbon atoms. 21.The circuit board of claim 20 wherein the elastomer contains 0.5 to 10weight percent of the cure site monomer units and 40 to 62 weight % ofmethyl or ethyl acrylate units.
 22. The circuit board of claim 15wherein the adhesive composition includes a catalyst promoting thereaction of the phenol-aldehyde and the 1,2-epoxy resin.
 23. The circuitboard of claim 20 where the catalyst is an imidazole.
 24. The circuitboard according to claim 15 wherein a portion of the ethylene-acrylicelastomer is replaced by a nitrile-based elastomer and wherein not over25% of the ethylene-acrylic elastomer is replaced by the nitrile basedelastomer.
 25. The circuit board according to claim 15 wherein theadhesive composition comprises:(a) 4-72% by weight phenol aldehyde or aresin from an unsaturated phenol; (b) 4-72% by weight 1,2-epoxy resin;(c) 10-80% by weight of a copolymer of ethylene, an alkyl acrylateselected from methyl and ethyl acrylate, and from about 0.5 to 10 weightpercent of a mono alkyl ester of 1,4-butene-diodic acid in which thealkyl group of the ester has 1 to 6 carbon atoms, said copolymer havingfrom about 20 to 35 grams of (--CO₂ --) units per 100 grams ofcopolymer, said copolymer having a melt index of about 0.3 to 100 g/10min.
 26. The circuit board of claim 25 wherein said mono alkyl ester of1,4-butene dioic acid is: methyl hydrogen maleate, ethyl hydrogenmaleate, or propyl hydrogen maleate.
 27. The circuit board of claim 26wherein the alkyl acrylate units comprise about 40 to 62% weight percentof the copolymer.
 28. The circuit board of claim 25 wherein (a) is aphenol-formaldehyde or cresol-formaldehyde resin.